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Usually people run their desktop system with X. But you can usually access true text-mode terminal, several of them actually. These are called virtual consoles. You can then normally login and use command-line, etc.

The power and flexibility of SSH never cease to amaze me.
Also the ability to make a raid array out of anything (floppies, anyone?), all the filesystems available, cool stuff like LVM, the crypto tools, the possibility of crafting your own tools with the myriad of compilers, interpreters, languages... Oh, and not forgetting getting new stuff installed with apt-get or similar.

I use bash color codes in my /root/.bash_profile to make my root bash prompt a different color than my non-root standard user prompt. Just one more reminder that I'm a single command away from destroying an entire system. ;)

I use nc (netcat) a lot to test things. Nice utility with a lot of versatility.

For the longest time I never knew that chown could accept both username and groupname together as an argument, i.e.: chown user:group -R /some/directory. That fact has saved me a lot of typing (no more chown/chgrp pairs).

The df command's a quick shortcut to see all your mounted filesystems.

I use pgrep a lot in scripts to see if a process is running.

kexec is pretty neat, lets you reboot without going through BIOS, which shortens reboot times significantly. Don't really reboot a lot, though...

Never used script(1) to save a terminal session?apg(1) to make random passwords
do you want to know how many processors/cores you have? nproc(1)sfdisk(8) great partition toolmultitail(1) multiple tail at once...great tool